The Influence Of Single-star Model In Gaia Astrometry On Binary Stars

Gaia survey is the most accurate astrometric project so far.Five dimensional parameters are provided by Gaia,including proper motion and parallax with high precision.This paper mainly studies in proper motion.The prope motion of binary stars are solved according to the single model.So,we discusses whether single model affect the parameters solution of binary.If it is,What will specifically changes to the binary parameters? This is the problem to be solved in this paper.We select 31 open clusters in Gaia Data Release 2(Gaia DR2)and Gaia Early Data Release 3(Gaia EDR3)as the research samples,and divide the open clusters into single and binary on the Color-Magnitude Diagram.In this paper,the statistical analysis method is used to study the difference of the proper motion distribution of single and binary.we analyze the proper motion distribution and the observation error distribution of single and binary in each open cluster by histogram.Gaussian fitting results with the apparent error and intrinsic error of proper motion are obtained by MCMC for single and binary.In Gaia DR2,it is found that proper motion's dispersion and observation distribution of binary is larger than single.The effect still exists Gaia EDR3.Based on Gaussian fitting result,it is concluded that the using single model will affect parameters of binary,and dispersion of binary larger than single in proper motion.Observation effect in Gaia makes proper motion dispersion of binary larger,which make it more difficult to study of mass segregation and determine the member stars.Especially,when we determine member stars by proper motion,we should consider this effect will influence the fraction of binary in the cluster.It is confirmed that the using single model to solve parameter of binary will make larger dispersion.It is a reminder that Gaia need to build a binary model in Astrometry solution.